1. Field of the Invention
The present invention generally relates to a thin film magnetic memory device and, more particularly, to a thin film magnetic memory device wherein magnetic memory cells forming separate memory cells are provided in proximity to each other.
2. Description of the Background Art
In recent years, research has been performed concerning MRAMs (Magnetic Random Access Memories) as next-generation semiconductor memory devices. As for the memory cell configuration of an MRAM, a so-called one transistor-one MTJ (Magnetic Tunnel Junction)-type MRAM configuration formed of a TMR (Tunneling MagnetoResistive) element, which includes a magnetic tunnel junction (MTJ), and of one transistor can be cited as an example. In a memory cell of such an MRAM, a digit line extends beneath the TMR element via an insulator film. In addition, a bit line extends in a manner that intersects the digit line so as to bring into contact with the top surface of the TMR element. Thus, a magnetic field generated by currents that are made to flow through the digit line and through the bit line is used so as to change the direction of magnetization in a ferromagnetic layer, which is a free layer forming a magnetic tunnel junction in the TMR element and, thereby, rewrite of data in the memory cell is carried out.
Respective TMR elements forming memory cells independent of each other, however, are provided in proximity to each other in order to achieve miniaturization of the MRAM. Therefore, a problem arises wherein an unexpected magnetic field is generated in a second TMR element adjacent to a first TMR element, which forms one memory cell, in the case where currents are made to flow through a digit line and through a bit line in order to generate a predetermined magnetic field in the first TMR element.
In addition, a magnetic memory device having the purpose of reducing the power consumption at the time of write-in is disclosed in Japanese Patent Laying-Open No. 2002-110938. The magnetic memory device disclosed in above literature is an MRAM and is formed of a magnetic memory element and a transistor. The magnetic memory element is provided with wires intersecting each other at right angles and a ferromagnetic double tunnel junction located at the location wherein these wires intersect each other. Each of the wires intersecting each other at right angles is provided with a magnetic film covering the side opposite to the side facing the ferromagnetic double tunnel junction, as well as the remaining sides, and the side of the wire that faces the ferromagnetic double tunnel junction is exposed from the magnetic film.
According to the magnetic memory device of such a configuration, in the case where a magnetic field for write-in is applied to one of two adjacent memory cells, the effects given to the other memory cell by this magnetic field can be reduced. Thereby, crosstalk generating between the two adjacent memory cells can be effectively prevented.
In the magnetic memory device disclosed in above literature, wires are covered with magnetic material and the magnetic material is utilized as a shield for suppressing the generation of crosstalk. In order to cover the wires with the magnetic film, first, a trench is formed in an interlayer insulating film and this trench is filled in with a magnetic material. Then, another trench for a wire is formed in the magnetic material and is filled in with a conductor film for a wire. In addition, according to another manufacturing method, a trench for a wire is formed in the interlayer insulating film and, at the same time, this trench for a wire is filled in with a magnetic material and a conductor film.
The pitch according to which the trenches are formed in the interlayer insulating film, however, cannot be reduced to a constant level, or less, due to limitations in the photolithographic process for the formation of trenches. On the other hand, it is necessary at present to reduce the pitch according to which the trenches are formed to be as small as possible because miniaturization of semiconductor devices is required. Because of these reasons, the pitch according to which the trenches are formed has been determined to be a predetermined value.
Under such conditions, the width of the wires is reduced by the thickness of the magnetic material in the case where the wires are covered with magnetic material and, then, the thickness of the magnetic material must be taken into consideration. In addition, the height of the wires is reduced by the thickness of the magnetic material in the same manner in the case where the height wherein trenches for a wire are formed is determined by a structure beneath the wires. In the case where the width of the wires and the height of the wires are reduced in the above described manner, the area of the cross section of the wires is reduced so as to increase the resistance of the wires. This increase in the resistance of the wires hinders currents that are made to flow through the digit line and through the bit line so as to generate magnetic fields and a problem arises wherein a sufficient magnetic field cannot be generated in the TMR element.
In addition, it becomes necessary to carry out a photolithographic exposure process twice in the case where a manufacturing method is adopted so that trenches are formed twice in the interlayer insulating film in order to cover the wires with a magnetic film. Therefore, a mask shift generates and a problem arises wherein the thickness of the shield made of the magnetic material differs depending on the locations of the wires. In addition, in the case where a manufacturing method is adopted so that a magnetic material and a conductor film are filled in at the same time, a problem arises wherein the thickness of the wires becomes uneven due to dispersion in the thickness of the magnetic material that is used for the initial fill in and the wires cannot be formed at predetermined locations.
Therefore, an object of the present invention is to solve the above described problem and to provide a thin film magnetic memory device wherein crosstalk generating between adjacent memory cells is suppressed and wherein the wire resistance is not increased.
A thin film magnetic memory device according to the present invention includes: first and second magnetic memory cells provided on a main surface of a semiconductor substrate at a predetermined distance away from each other so as to operate as memory cells; a first wire for applying a magnetic field to the first magnetic memory cell extending in one direction so as to intersect the first magnetic memory cell; a second wire for applying a magnetic field to the second magnetic memory cell extending in parallel to the first wire so as to intersect the second magnetic memory cell; and a magnetic film provided so as to fill in the space between the first wire and the second wire and so as to bring into contact with the first and second wires.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.